The repeated low doses of UVB protected to a limited extent against the effects of an erythemal UVB dose on cytokine expression and thymine dimer formation, but not on CHS or COX enzymes.

Although it is generally recognised that UV radiation (UVR) can induce suppression of contact hypersensitivity (CHS) in human subjects, most protocols to date have not tested the effect of low daily doses of solar simulated radiation (SSR). In the present study, healthy individuals, divided into four groups each consisting of approximately 34 subjects, were whole-body irradiated with 1.2 standard erythema doses of SSR for 2, 10 or 30 consecutive days, or were unirradiated. They were sensitised with diphenylocyclopropenone (DPCP) on one exposed body site 24 h after the final UVR. The occurrence and severity of the primary allergic response were noted, and both parameters were shown to be significantly lowered in the group irradiated for 30 days compared with the unirradiated group. Elicitation of CHS was undertaken 3 weeks after the sensitisation, using a range of concentrations of DPCP on a UV-protected body site. The extent of the CHS at 48 h was assessed by the clinical score, by an erythema meter and by histological examination of a biopsy taken from the site challenged with one selected concentration of DPCP. Although erythema and pigmentation did not differ between the groups, a significant negative correlation was found between the clinical CHS score and the number of days of UV exposure, at the lowest challenge dose of DPCP. In addition a significant negative correlation was revealed between the intensity of spongiosis (intraepidermal oedema and vesicles, as evaluated by histology) and the number of days of UV exposure. Thus small daily doses of SSR induce suppression of CHS in human subjects and the effect is cumulative, indicating that there is no adaptation to the immunomodulating effects of UVR, at least over the test period of 30 days.

The aim of our study was to compare serum concentration of IL-1β, IL-6, IL-8, IL-10, and TNF-α in 105 healthy volunteers before and after exposure to UVR: 25 subjects (10 days of UVB), 55 (10 days of UVB or solar-simulated radiation, followed by acute UVB dose), and 25 (local high dose of UVB). In all the individuals blood samples were analyzed before and after final irradiation by chemiluminescence assay. After 10 days of UVB irradiation a statistically significant increase in serum concentration only in IL-8 (P < .05) and strong tendency in TNF-α (P = .05) were observed. The applied schedules of irradiation have minor impact on serum cytokine level and still a threshold dose of UVR causing systemic immune impairment is unknown.

Exposure to ultraviolet radiation causes alterations of cutaneous and systemic immunity. The aim of our study was to assess the influence of low doses of solarsimulated radiation (SSR) on the phenotypes of blood dendritic cells (BDC). Healthy volunteers (94) were irradiated with a dose of 1.2 SED (standard erythema dose) of SSR for 2, 10 or 30 consecutive days. Blood samples were taken before the first exposure and 24 h after final exposure. The three main subsets of BDC were distinguished by flow cytometry:. The percentage of total DC was elevated in all groups by the UV exposure and was significantly increased after 2 and 30 days of irradiation (P ¼ 0.006 and P ¼ 0.018, respectively). A particularly distinct increase was observed in the percentage of the MDC1 after 2 and 30 days (P ¼ 0.022 and P < 0.0001, respectively). The MDC2 showed an increase after 10 days and a subsequent significant decrease after 30 days of irradiation (P ¼ 0.031). A significant increase in PDC was found after 2 days of irradiation (P ¼ 0.0006). Exposure to SSR induced an increase in the percentage of BDC in healthy human individuals, especially apparent in the MDC1 subtype.

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